Fuel amount control

Abstract

A method and a device of controlling the amount of fuel delivered to a combustion engine (1), e.g. of two-stroke or four-stroke type, wherein the fuel is supplied through an intake passage (2) intended to deliver air (3) and fuel (4) to the cylinder (5), said intake passage being opened and closed by a piston (6) or by a special valve (7). The fuel supply to the intake passage (2) is effected upstream from the piston (6) or the valve (7) and in response to the opening and closing of the intake passage (2) varying flow speeds and pressures are produced in the passage and the fuel supply system (8) is of a kind the supply amount of which is substantially affected by this variation, such as a carburetor (9) or a low-pressure injection system (10). In order to regulate the fuel supply to the engine fuel a brief cut-off takes place in the fuel-supply system (8) of the entire fuel flow or the part flow and the brief cut-off is arranged to take place to an essential extent during a part of the engine revolution when the intake passage is closed and the fuel supply accordingly is reduced or has ceased.

I claim: 
     
       1. A method of controlling the amount of fuel delivered to a combustion engine (1), wherein the fuel is supplied through an intake passage (2) intended to deliver air (3) and fuel (4) to one cylinder (5), said intake passage being opened and closed by a piston (6) and wherein the fuel supply to the intake passage (2) is effected upstream from the piston (6) and wherein, in response to the opening and closing of the intake passage (2), varying flow speeds and pressures are produced in the intake passage, the fuel supply system (8) being substantially affected by this variation and, in order to regulate the fuel supply to the engine, a cut-off takes place in the fuel-supply system (8) during a portion of the operating cycle by a shut-off valve (24; 17) which shuts off at least a part of the fuel flow, wherein a change of the state of the shut-off valve (24; 17) is arranged to take place during the cylinder suction phase, whereas a change of state associated with this change, essentially takes place outside the cylinder suction phase, so that fuel supply regulation takes place essentially in conjunction with one of the changes of state of said shut-off valve (24; 17). 
     
     
       2. A method as claimed in claim 1, wherein the shut-off valve (24; 17) is operable to shut off the entire fuel flow during a portion of the operating cycle to regulate the fuel supply to the engine. 
     
     
       3. A method as claimed in claim 1, wherein the fuel supply system (8) is a carburetor type (9) system. 
     
     
       4. A method as claimed in claim 1, wherein the cut-off is arranged to prevent fuel supply (34, 35) to the intake passage (2) caused by oscillation phenomena arising in connection with the closure of the intake passage by the piston. 
     
     
       5. A method according to claim 1, wherein the cut-off is arranged to start before the piston (6) has closed the intake passage (2), and is arranged to cease essentially before the piston (6) again begins to open the intake passage (2). 
     
     
       6. A method as claimed in claim 1, wherein the cut-off begins only after closure of the intake passage (2) by the piston (6), and wherein the cut-off ends only after the intake passage has again been opened by the piston (6). 
     
     
       7. A method as claimed in claim 1, wherein the cut-off is effected only on non-consecutive occasions. 
     
     
       8. A method as claimed in claim 1, wherein the shut-off valve (24) is operated electrically, and is of a normally open type, and wherein cut-off is effected by supply of current to the valve. 
     
     
       9. A device to control the amount of fuel supplied to an engine (1), wherein the fuel is delivered through an intake passage (2) intended to deliver air (3) and fuel (4) to one cylinder (5), said intake passage being opened and closed by a piston (6) and wherein the fuel supply to the intake passage (2) is effected upstream from the piston (6) and wherein, in response to opening and closing of the intake passage (2), varying flow speeds and pressures are produced in the intake passage, the fuel supply system (8) being operable to supply different amounts of fuel in response to the flow speeds and pressures in said intake passage and includes a shut-off valve (24; 17) which at least partially cuts off the fuel supply flow during a portion of the operating cycle, and a change of the state of the shut-off valve (24; 17) takes place during the cylinder suction phase whereas a change of state associated with this change essentially takes place outside the cylinder suction phase, so that fuel supply regulation takes place in conjunction with one of the changes of state of said shut-off valve (24; 17), and means for opening and closing the shut-off valve in response to the engine revolution position. 
     
     
       10. A device as claimed in claim 9, wherein the shut-off valve (24) is electrically controlled and is a normally open type of valve. 
     
     
       11. A device as claimed in claim 9, wherein the shut-off valve (24) is electrically controlled and closing of the shut-off valve is commanded only on non-consecutive occasions. 
     
     
       12. A device as claimed in claim 9, wherein the fuel supply system (8) is a carburetor (9) comprising at least one fuel supply line (25) leading to a low-speed nozzle and at least one fuel supply line (26) leading to a high-speed nozzle, said lines merge in a common line (26) and the shut-off valve (24) is arranged to shut off said common line (26). 
     
     
       13. A device as claimed in claim 9, wherein the fuel supply system (8) is a carburetor (9) comprising at least one fuel supply line (25) leading to a low-speed nozzle and at least one fuel supply line (26) leading to a high-speed nozzle, the shut-off valve is arranged to shut off both lines (25, 26) simultaneously.